Python使用metaclass实现Singleton模式的方法

class Singleton(type):
def __call__(cls, *args, **kwargs):
print "Singleton call"
if not hasattr(cls, 'instance'):
cls.instance = super(Singleton, cls).__call__(*args, **kwargs)
return cls.instance
def __new__(cls, name, bases, dct):
print "Singleton new"
return type.__new__(cls, name, bases, dct)
def __init__(cls, name, bases, dct):
print "Singleton init"
super(Singleton, cls).__init__(name, bases, dct)
class Cache(object):
__metaclass__ = Singleton
def __new__(cls, *args, **kwargs):
print "Cache new"
return object.__new__(cls, *args, **kwargs)
def __init__(cls, *args, **kwargs):
print "Cache init"
def __call__(cls, *args, **kwargs):
print "Cache call"
print Cache()
print Cache()

输出：

Singleton new
Singleton init
Singleton call
Cache new
Cache init
<__main__.Cache object at 0x01CDB130>
Singleton call
<__main__.Cache object at 0x01CDB130>

希望本文所述对大家的Python程序设计有所帮助。

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